Dušan Bakoš

Poly(vinyl alcohol) stabilisation in thermoplastic processing

Besides casting from water solutions, PVA processing from the melt seems to be more suitable, particularly for water-soluble films. Processing at high temperatures is very sensitive to PVA degradation and problems with stability of the melt result in a search for suitable additives. Silica is frequently used as an antiblock agent and only a little is known about its effect on PVA melt stability. The study was focused on PVA thermal and processing stability. and an evaluation of low molecular products released as by-products of PVA degradation. It was found that the thermal stability of PVA is strongly influenced by the pH of the environment before drying in the production process. Processing stability of PVA blends with and without glycerol used as plasticiser were evaluated from the torque increase during processing. Regarding the effect of the antiblock agents, silica had a strong negative effect on processing stability of PVA. In contrast, talc did not accelerate degradation up to a relatively high concentration level. To explain these effects, the changes in chemical structure of PVA blown films during thermal loading were studied using IR spectroscopy. It was confirmed that silica accelerates thermal degradation of PVA films due to its acidic character.

Poly(vinyl alcohol)–collagen hydrolysate thermoplastic blends: I. Experimental design optimisation and biodegradation behaviour

Abstract Hybrid blends based on poly(vinyl alcohol) (PVA) and collagen hydrolysate (CH), an abundant, added value waste product of the leather industry, have been processed by melt blow extrusion to environmentally degradable films. Optimisation of the blend compositions was performed in respect of mechanical properties of the films. The experimental design method (DOE) was used for the understanding of the structure–property relationships in the hybrid blends using glycerol as a plasticiser. Parameters were selected from torque measurements, melt flow index, thermogravimetric analysis, as well as tensile strength and elongation at break of the plasticised blends. The use of the DOE method offers the possibility of identifying a range of blend compositions suitable to yield products with valuable mechanical and thermal properties. Biodegradation experiments performed under anaerobic conditions evidenced a positive effect of collagen hydrolysate on the mineralization rate of PVA/CH blends.

Assessing biodegradability of plastics based on poly(vinyl alcohol) and protein wastes

Research was conducted into biodegradability of mixed polymer films based on poly(vinyl alcohol), protein hydrolyzate (collagen hydrolyzate from wastes after chrome tanning) and glycerol in an aqueous aerobic environment. Evaluation of biodegradation was based on carbon dioxide produced in the gas phase. Pure PVAL was degraded by a current mixed culture for water-treatment (unadapted) only after an approx. 10-day lag phase; during breakdown of mixed film the protein component and glycerol were broken down first and PVAL degradation occurred in the second stage. Biodegradation could be well described by 1st-order formal chemical kinetics. Repeated degradation by an adapted culture proceeded in a single stage with considerably shorter lag phase (<30 h) at a simultaneously approx. 1.5-fold greater breakdown rate (rate constants). During degradation of substrates containing PVAL, microbiological tests proved an approx. 100-fold increase in numbers of PVAL-degrading bacteria. Added protein hydrolyzate + glycerol in PVAL contributed to increasing biodegradability more than followed from proportional representation of individual components.

Poly(vinyl alcohol)–collagen hydrolysate thermoplastic blends: II. Water penetration and biodegradability of melt extruded films

Abstract Water solubility of polyvinyl alcohol (PVA) is related to degree of hydrolysis, molecular weight and modification during blending in the presence of other processing additives. In the present paper the effect of collagen hydrolysate (CH), an abundant waste product of the leather industry, and glycerol on PVA water sensitivity has been investigated. This study is a continuation of the previous research on experimental design optimisation of PVA-collagen hydrolysate blends (P. Alexy, D. Bakos, S. Hanzelova, L. Kukolikova, J. Kupec, K. Charvatova, E. Chiellini, P. Cinelli, Polymer Testing 2003, 22 doi:10.1016/S0142-9418(03)00016-3) . CH content affects water penetration into the prepared blown films, affecting therefore their solubility. An increasing content of CH in PVA based blends shortens the time to the first disruption of the film after immersing in water, restraining the negative effect of glycerol on solubility. Water penetration into film is influenced by both added components—glycerol and CH, and mutual effects depend upon their proportional amounts in the blends. Pure PVA film presented limited biodegradation at low temperature (5 °C). The CH addition in the blend significantly increases biodegradation rate at that temperature. PVA/CH blends properties are of practical relevance for applications as hospital laundry bags and containers of water-soluble substances, such as chemical agents for treatment of waste and potable water, fertilizers, washing agents, sanitary products, etc.

Blends of polyvinylalcohol with collagen hydrolysate : Thermal degradation and processing properties

The blends of polyvinylalcohol with collagen hydrolysate were studied from the point of view of the effect of collagen hydrolysate on thermal degradation and processing properties. Elimination of deliberated acetic acid in reaction with NH 2 groups of CH can protect PVA against acidic catalysis of degradation. Using talc instead of silica can eliminate the crossliking effect in PVA-CH-silica blend when silica is used as antiblock agent. The obtained results make possible to use PVA/CH blends for blowing of biodegradable films with CH content up to 30 wt.%.

Blends of polyvinylalcohol with collagen hydrolysate: properties of water-soluble blown films

The study is focused on the effect of collagen hydrolysate and glycerol on properties of water-soluble polyvinylalcohol (PVA) blown films and blends. The experimental design method (DOE) was used in this study. Results from DOE show a strong effect of interactions between the blend components on resulting properties of the films. This fact was confirmed by means of the response surfaces of melting flow index, tensile strength and the content of insoluble fraction. It was concluded that the composition of PVA/CH blend must be precisely specified to avoid the processing complications.

Chitosan Polyelectrolyte Complexes for Use in Tissue Engineering and Drug Delivery

The paper presents the first part of the work focused on preparation of biodegradable chitosan microcapsules with tailored properties for potential applications in medical field as drug temporary carriers. In this paper, we aimed to prepare chitosan and chondroitin sulphate microcapsules using TPP as the second cross-linker and investigate the formation of the capsule membrane and its permeability in dependence on conditions of polyionic complexation. As a model, TPP was used to assess an influence of concentration and reaction time on the microcapsule formation. The method of inverse SEC was used for pores size and permeability limit of capsules assessment. For chitosan/CHS/TPP capsules, the distribution of pores size in the membrane is rather broad, which can be suitable for applications in tissue engineering and drug delivery systems.